1. Field of the Invention
The present invention relates to an aliphatic ring-containing polymer that contains a sulfonyl group as the constitutive group of the ring skeleton thereof and to a method for producing the polymer, as well as to a resin composition for optical material, a shaped article, an optical material and a lens comprising the polymer. In particular, the invention relates to an optical material and a lens having a high refractivity, a high Abbe's number, a high-level heat resistance, a high-level light transmittance and a low water absorption, and to a resin material for producing them. The invention is applicable, for example, to optical parts such as lenses for spectacles, lenses for optical instruments, lenses for optoelectronics, laser lenses, pickup lenses, in-vehicle camera lenses, mobile camera lenses, digital camera lenses, OHP lenses, lenses constituting microlens arrays, etc.
2. Description of the Related Art
As compared with glass, a transparent resin material has various advantages in that it is excellent in lightweightness, impact resistance and shapability and is economical; and recently, resin is being much used for optical glass in the art of optical parts such as lenses and others.
One typical transparent thermoplastic resin material is a polycarbonate resin. In particular, a polycarbonate resin produced by the use of 2,2-bis(4-hydroxyphenyl)propane (generally called bisphenol A) as a starting material has many advantages in that it is excellent in transparency, more lightweight than glass and excellent in impact resistance and that it is applicable to industrial-scale mass-production of shaped articles as being able to be shaped in melt; and therefore the resin of the type is being much used as optical parts in various fields. The resin has a relatively high refractive index of 1.58 or so, but its Abbe's number indicating the degree of refractivity dispersiveness is around 30 and is low, or that is, the resin is poor in the balance between the refractivity and the dispersiveness characteristic thereof. At present, therefore, the resin is limited in point of the range of its applications to optical parts. For example, regarding lenses for spectacles that are one typical example of optical parts, it is known that the materials for those lenses preferably have an Abbe's number of at least 40 when the visibility function thereof is taken into consideration (Non-Patent Reference 1); and in case where a polycarbonate resin produced by the use of bisphenol A as a starting material is directly used for those lenses as it is, the lenses formed of the resin could hardly have the desired characteristics.
According to Non-Patent Reference 2, the aberration occurring inside the optical system of imaging instruments include monochromatic aberration such as spherical aberration, coma aberration, astigmatism, distortion and field aberration, and chromatic aberration. In particular, when chromatic aberration is large, then color fringing may be large with the result that the image quality of color images may greatly worsen. The non-patent reference says that the chromatic aberration of the type can be corrected by a combination of lenses where a lens having a high refractivity and a lens having a large Abbe's number are combined.
As an optical resin material having a large Abbe's number, known is a cyclic olefin resin comprising a total hydrocarbon. The Abbe's number of the cyclic olefin resin is from 50 to 57 or so and is relatively high, however, the refractive index thereof is not so high; and those of which both the Abbe's number and the refractive index are high are not as yet provided. With the recent tendency toward lightweight and small-sized portable appliances, materials having a further higher refractive index are desired, and resins more excellent than cyclic olefin resins are needed.
As a resin containing a sulfur atom, for example, Patent Reference 1 describes a polymer prepared through metathesis polymerization of an aliphatic cyclic olefin that contains a sulfur atom as the constitutive atom of the ring skeleton thereof. Using the polymer realizes a relatively high refractive index of from 1.58 to 1.59, but could not attain a high Abbe's number of at least 50. In addition, the patent reference describes nothing relating to introduction of a sulfonyl group as the constitutive group of the ring skeleton.
On the other hand, Patent Reference 2 says that use of a (meth)acrylate having a sulfonyl group-containing heterocyclic skeleton as a resin material provides a lens having a high refractive index and a high Abbe's number. The polymer has a refractive index of from 1.51 to 1.52 and an Abbe's number of from 60 to 61; however, its practical use is problematic since its water absorption is high.
For these reasons, heretofore, even when a sulfur atom-containing resin is used, all the requirements of high refractivity, high Abbe's number and low water absorption could not be satisfied.
On the other hand, some polymers similar to the polymer of the invention in point of the structure thereof have been proposed.
For example, Patent Reference 3 describes a polymer prepared through copolymerization of an aliphatic polycyclic olefin optionally substituted with a functional group and a polar vinyl olefin. The patent reference describes various types of functional groups as the substituent, showing a sulfonylalkyl group among them. However, the patent reference describes nothing relating to production examples and physical data of sulfonylalkyl group-having polymers, and describes nothing relating to the applicability of the polymers to lenses. In addition, in this, since the sulfonyl group is not a constitutive group of the ring structure of the polymer, the polymer therein differs from the polymer of the invention in point of the structure thereof.
Patent References 4 and 5 describe resins prepared through polymerization of a polycyclic olefin. They say that use of the resin can realize high refractivity, high Abbe's number and high-level heat resistance. However, these references do not describe an aliphatic ring-containing polymer that contains a sulfonyl group as the constitutive group of the ring skeleton thereof. In addition, in Patent Reference 4, use of inorganic fine particles as mixed in the resin is needed, and in Patent Reference 5, use of a fluorine atom-substituted polycyclic polymer is needed; or in other words, the resins in these patent references are limited in point of the usage pattern thereof. Further, from the viewpoint of providing a resin material capable of satisfying all the requirements of high refractivity, high Abbe's number, high-level heat resistance, high-level light transmittance and low water absorption, there is room for further development    Patent Reference 1: JP-A 2007-9178    Patent Reference 2: WO2006/075646    Patent Reference 3: JP-T 2008-519882    Patent Reference 4: JP-A 2010-77280    Patent Reference 5: JP-A 2010-145959    Non-Patent Reference 1: Quarterly Journal of Chemical Review, No. 39, Refractivity Control of Transparent Polymer, edited by the Chemical Society of Japan    Non-Patent Reference 2: Technology and Application of Plastic Lenses, published by CMC (2003)